Different %s format behaviour in Lua 5.2 beta vs Lua 5.1
Quite some time ago, there was a discussion about whether
('%s'):format and table.concat should call tostring if something it
must act on is not a string. Roberto  thought yes for the former,
no for the latter.
The Lua 5.2 beta documentation does not say so, but the behaviour of
`('%s'):format` in Lua 5.2 beta has indeed been modified accordingly.
Maybe it is worth half a sentence in the manual:
- The options c, d, E, e, f, g, G, i, o, u, X, and x all expect a
number as argument, whereas q and s expect a string.
+ The options c, d, E, e, f, g, G, i, o, u, X, and x all expect a
number as argument, whereas q expects a string and s coerces its
argument to a string by calling tostring.